The present invention relates generally to a method for charging coal into a coke oven through a pipeline and more particularly to a method for doing so in such a manner as to minimize the amount of coal fines which are removed from the coke oven through an exhaust conduit during the charging operation.
Typically, a coke oven has two opposite ends, both provided with doors. One end is a pusher end through which a ram or pusher is introduced for pushing coke toward the opposite, discharge end, also called the coke side.
Methods and apparatus for charging coal into a coke oven through a pipeline are disclosed in Auvil U.S. Pat. No. 3,761,360, which discloses pipeline charging through the end wall of the coke oven, and in Schmidt U.S. Pat. No. 3,047,473 which discloses pipeline charging through the top of the coke oven.
Generally, in the pipeline charging of coke ovens as disclosed in Auvil U.S. Pat. No. 3,761,360, coal is entrained with a carrier gas such as steam and conducted through a main pipeline extending alongside a battery of coke ovens. A branch pipeline extends from the main pipeline to the pusher end of each coke oven and directs the mixture of coal and steam into the coke oven through an entry in the pusher end near the top thereof. Near the opposite end of the coke oven, in the roof thereof, is an exhaust opening, and, during the charging operation, there is an unavoidable discharge of coal fines through the exhaust opening. This is commonly referred to as fines carryover. Fines carryover is undesirable, and is a problem which must be minimized.
The problem of fines carryover is especially prevalent at the beginning and end of the charging operation.
More specifically, the temperature of the coke oven is substantially higher than the temperature of the coal particles entering the oven during charging, and the increased temperature in the coke oven causes volatilization of the coal particles. The volatile gases given off from the coal, as well as the carrier gas utilized to conduct the coal to the coke oven through the pipeline, are exhausted from the coke oven through the exhaust opening at the end of the coke oven. The greater the amount of gases in the coke oven, the greater the pressure in the coke oven and the greater the exhaust effect. It is believed that the greater the exhaust effect, the greater the amount of fines carryover. Volatilization of the coal particles and the amount of gas resulting therefrom is greatest at the beginning of the charging operation.
In the prior art end-charging method, one attempt to overcome the problem of fines carryover was to vent some of the carrier gas from the mixture of coal and carrier gas, just prior to entry of the mixture into the coke oven, thereby reducing the amount of gases in the coke oven.
There is a zone adjacent the exhaust outlet where the exhaust effect is so great that any particle entering that zone will be blown or forced out of the coke oven. The fines carryover problem at the beginning of the charging operation and, to some extent, throughout the charging operation, is aggravated when coal particles are directed or rebound toward that exhaust zone.
The problem of increased fines carryover near the end of the charging operation arises from the following considerations. There is a moving gas stream within the coke oven normally proceeding from the entry end of the coke oven to the exhaust outlet. As the level of the coal bed in the coke oven rises, the velocity of the gas stream moving from the entry end of the coke oven to the exhaust end of the coke oven increases. This is because the cross sectional area of the oven through which the gas can flow decreases as the coal bed rises in the oven, thereby increasing the velocity of the gas stream which is being exhausted from the coke oven. The increased velocity of the gas stream moving toward the exhaust outlet tends to carry with it newly introduced coal particles from the mixture of coal and carrier gas, exhausting these particles before the particles have a chance to settle out from the mixture onto the bed of coal.